BAGHDAD, Iraq (CNN) -- Two civilian drivers in northern Iraq were killed in incidents involving U.S. troops, one in an "escalation of force" shooting and the other in a head-on collision, the military said Saturday.

The shooting occurred Friday between Tikrit and Balad when a military convoy "stopped on a rural road after one of its vehicles broke down."

Troops tried to signal the truck to halt, but the truck "continued to accelerate as it drew closer to the convoy."

"A U.S. soldier perceived a threat and engaged the truck after the driver did not respond to warnings to stop, as the truck approached a halted U.S. logistics convoy from the rear," the military said.

The truck driver was then shot and killed.

"It's a tragic event, but the soldier perceived a threat. He was protecting the convoy against what he thought was an attack and did so in accordance with the security agreement, " said Maj. Derrick Cheng, spokesman for Multi-National Division North, referring to the bilateral U.S.-Iraqi security pact.

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The military said a teen passenger in the vehicle was unharmed, and a U.S.-Iraqi investigation has begun.

The other incident occurred Thursday near Khalis.

A driver died in a "head-on collision" with a U.S. Army Stryker vehicle, the military said.

The car struck the lead vehicle of a combined U.S. forces and Iraqi Army convoy as it was returning to a forward operating base after a patrol.

"According to reports, the convoy slowed its speed to approximately 30 mph and moved to the shoulder of the road to allow the oncoming car room to pass. However, the car hit the lead vehicle head-on, killing the driver and injuring at least one soldier inside the Stryker."

The Stryker driver tried to signal the car with headlights and horns but "the car did not alter its speed or bearing." This incident is also under investigation by U.S. and Iraqi forces.

Meanwhile, at least five Iraqis were killed and 35 others wounded when a car bomb exploded in northern Iraq on Saturday, an Interior Ministry official said.

The bomb detonated in Kogjili, a predominantly Shiite Shabak area of eastern Mosul. Most Shabak people are Shiites, and live in Nineveh province. They are one of Iraq's minority groups.

A spate of bombings Wednesday and Thursday near Mosul, the capital of Nineveh province, and in the town of Tal Afar left at least 50 people dead and many others wounded.

Al Qaeda in Iraq -- a predominantly Sunni militant group -- maintains a presence in the region.

In central Baghdad, at least two people were killed and 11 others wounded when two bombs went off Saturday, the official said.

One bomb was placed outside a pool hall and the other targeted a police convoy.

In another attack in southwestern Baghdad Saturday evening, a bomb inside a man's car exploded, killing him and wounding a dozen others, the Interior Ministry official said.

The man was employed by the Council of Ministers, Iraq's Cabinet, the official said.

The man's wife was among those wounded in the attack in the al-Saydiya neighborhood, the official said.